In use in popular ignition systems for internal combustion engines is an ignition coil or coils having a C-shaped iron core within a non-conductive housing, with the primary and secondary windings wound on individual bobbins inter-nested within one another and lying within the boundaries of the C-shaped iron core. The coil is filled with epoxy potting material or other insulating material as a final step in the process. Despite being filled with epoxy, the gap between the ends of the legs of the C-shaped iron core are referred to as an "air gap". It is also known that the efficiency can be increased and compactness of the overall coil structure, including the housing, can be reduced by nearly filling the air gap portion of the aforementioned iron core with a permanent magnet. Such a coil construction is shown in U.S. Pat. No. 4,990,881. Part of the success in making such a coil design commercially practical has been the discovery of a very strong permanent magnetic material containing such elements as samarium (Sm), neodymium (Nd), and other similar rare earth, high energy materials. The permanent magnet used is made entirely of such material and referred to as "fully dense". The air gap of the iron core of the ignition coil, although reduced by insertion of the magnet, is still retained in the design of the aforementioned coil.
In contrast, in the subject invention a permanent magnet-type ignition coil is provided having preferably no air gap and also assuring that should there be a small air gap due to component tolerance stack-up it will be in a predetermined location thereby enhancing considerably the efficiency and power output of the coil. This allows for a substantial reduction in the size of the overall unit for acquiring the same unit power output. A further feature of the subject invention is the design and use of a permanent magnet composed of a bonded magnetic material, which is less than fully dense, made of these most recently available rare earth, high energy materials such as samarium and neodymium, thereby providing a material which is equally effective, but far less expensive than the fully dense permanent magnet heretofore used, and having the added benefit that its thickness, including the magnetizing alloy elements Nd or Sm or equivalent, provides for less expensive fabrication and easier handling during assembly of the coil.
Additionally, it is clear from the prior art that little thought has been given to developing a modularly constructed ignition coil whereby with minor reconstruction of several components the same coil may be used for at least two separate ignition strategies, the first strategy requiring a high energy output suitable for use in a single strike ignition per combustion event within the combustion chamber, and the second ignition strategy requiring a significantly lower energy output and suitable for use in a rapid re-striking, multiple strike, ignition per combustion event.